×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Scan angle of an antenna array

Scan angle of an antenna array

Scan angle of an antenna array

(OP)
Hey guys, just a brief(ish) question regarding the scan angle of an antenna array ... as far as I understand it, the scan angle is the angle with respect to the axis of the array where you get maximum gain, i.e. the direction in which the main lobe of the pattern is directed. Is this correct?

Also, I realise that to prevent grating lobes appearing in the radiation pattern you should have an element spacing of <lamda/2, but if it isn't possible to keep the element spacing this low I was trying to determine what the effect would be on the scan angle. I think the following equation relates element spacing and scan angle:

element spacing < lamda/(sin(theta)+1)

, where the array is required to scan over a scan volume of plus/minus theta.

Say the element spacing is equal to 0.7*lamda, this gives a value of 25.4 degrees for theta; does this mean that the array will only be able to scan to an angle of plus or minus 25.4 degrees from it's axis and therefore not permit broadside radiation? I think my understanding of this may be a bit flawed, would anyone be able to explain this further maybe?

RE: Scan angle of an antenna array

Broadside radiation is ALWAYS possible by simply feeding the array elements in phase.


 

RE: Scan angle of an antenna array

when you scan that far, another beam pops up from imaginary space from the opposite direction of your scan. i.e. scan to +25 degrees and at -90 degrees, a second beam starts to be formed. So your original beam starts to drop in amplitude and it looks like a far away sidelobe starts to grow. Active VSWR suckouts start to be a serious concern too, you can get some energy trapped on the surface and burn up an array. That's why giant high power arrays have fire suppression systems.

Your max. angle scan can be increased by having elements whose individual patterns rolloff in one plane. Like a V pole wave guide element scanned in hpole plane, the pattern of the element rolls off alot in the hplane and if you overscan scan that direction, you won't lose too much gain until the individual waveguide element's pattern increases.

check out Pozars books, lots of good info there. Mostly about patch antenna arrays.

k

RE: Scan angle of an antenna array

(OP)
Thanks for your help guys (or girls of course!).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources